Our body has its own internal clock, or circadian rhythms, that signals when to stay awake and when to sleep but when we have long flights where we cross several time zones, this clock finds it difficult to sync. In this case, our body clock functions in accordance with the original time zone, instead of the time zone where we travelled. As a result, travellers are affected by jet lag that can cause daytime fatigue, an unwell feeling, difficulty in staying alert as well as gastrointestinal...
https://safety4sea.com/cm-understanding-fatigue-how-to-avoid-jet-lag/